1. Field of the Invention
Embodiments of the present invention are directed toward the field of integrated circuit devices and packaging related to power management systems.
2. Related Art
Varieties of integrated circuits are commercially available to facilitate power management tasks, for example, to control DC to DC voltage conversion or as a constant current controller.
DC/DC converter circuits are commonly used as Point Of Load (POL) power sources to drive a wide variety of semiconductor devices from a single “bulk” voltage routed around a system, for example, in an intermediate bus architecture (IBA). Generally, POL converter circuits are placed right alongside each semiconductor device and shift a single IBA voltage to the different voltage levels required by each integrated circuit. Typically, DC/DC converters drive such devices as FPGAs, microprocessors, DSPs, ADCs, SDRAMs, up/down converters, etc.
DC/DC converter circuits are also frequently used in systems comprising rechargeable batteries. Theses applications are characterized by portability (size, weight, etc.) and length of service from a single charge. For example, the efficiency of the DC/DC converter circuit directly affects the standby and talk time available from a cell phone between battery charges.
Current control products generally fall into two categories: constant current controllers and constant current sources. A constant current controller accepts a constant DC voltage and converts it to a constant current output. When the input voltage is subject to variation or instability a DC/DC converter is first used to steady the DC voltage and then the constant current controller takes that steady voltage and puts out a constant current. A constant current source generally comprises a DC/DC converter and a constant current controller.
DC/DC converters and current controllers offered by many integrated circuit (IC) manufacturers are silicon chips that provide only the basic operation for circuit functions. An end user must then select up to about 22 other components that surround the integrated circuit in order to create a complete circuit solution. The selection of these components and the circuit board layout affect the final performance in such critical areas as efficiency, ripple voltage, reliability, etc. Unfortunately, these critical features as defined by the integrated circuit manufacturer may not be the same as the performance features achieved when the customer completes the circuit on the board with the addition of external components. Consequently, because the user's assemblage of parts does not become a complete circuit function until the first time all parts come together, e.g., on a printed circuit board, the function must be tested as a subsystem function on the board.
Vishay Intertechnology, Inc., of Malvern, Pa., currently offers several versions of the FunctionPAK® DC/DC converters and current control modules. FunctionPAK® products are complete power management systems in single surface mount, e.g., BGA, packages. Advantageously, this product is a complete power management function in a single module. The single package contains all circuit components and is fully tested with all circuit parameters defined exactly as used in the customer's system.
FunctionPAK® power management products generally comprise multi-chip module (MCM) circuit packaging. In general, the term MCM refers to a package comprising two or more circuit elements, usually including at least one integrated circuit, and an interconnecting substrate to couple the circuit elements and the package contacts. MCM devices conventionally include, for example, laminated substrates, e.g., FR4 printed circuit boards, thin film depositions, surface laminar circuitry (SLC) and/or ceramic substrates.
FIG. 1A illustrates a top view of an exemplary MCM comprising many separate chip devices, passive components and other items mounted on a multilayer printed circuit board (PCB). For example, the exemplary MCM comprises an integrated circuit device 1, an inductor 2, a plurality of passive components, e.g., resistors and/or capacitors, 3, and a multilayer printed circuit board (PCB) 4. The devices and printed circuit board can be molded in plastic producing a single package. FIG. 1A also shows a side sectional view of components molded in plastic encapsulant 5.
FIG. 1B illustrates another top view of an exemplary MCM.
FIG. 1C illustrates a bottom view of an exemplary PCB for use in a multi-chip module that utilizes a ball grid array (BGA) packaging technique. FIG. 1C illustrates an exemplary ball grid array ball 6, used as a package contact to couple circuitry of the multi-chip module to a next electronic assembly, e.g., other components mounted to a processor “mother” board. FIG. 1C illustrates an exemplary wiring trace 7, which serves to couple the various components of the MCM and the package contacts, e.g., “balls.”
FunctionPAK® or MCM provides complete solutions and offers many advantages, e.g., the MCM saves space and weight, simplifies end product design/development, reduces component count, reduces assembly costs and saves test time, and speeds time-to-market.
The current FunctionPAK® power management products based on MCM design may, in some instances, have several electrical and thermal limitations as follows: 1) undesirable parasitic resistance due to thin copper layer; 2) undesirable parasitic inductance due to the pins of the package; limited current carrying capacity; 3) undesirable decreased efficiency due to the combined effects from the parasitic and the poor thermal performance; 4) undesirable power density because packaged silicon devices (control driver and power MOSFETs) are used which are encapsulated in a poor thermal conductive mold material; 5) undesirable switching frequency due to high switching loss, which limits the operating temperature and current rating; and 6) undesirable thermal performance due to poor thermal conductivity of the materials used. In addition, the design of the FunctionPAK® MCM using a multilayer PCB as a substrate with BGA re-routed connections may provide poor thermal efficiency and poor heat sinking. As a result, the operation and reliability of the circuit and active devices can be impacted. As discussed above, when the MCM is molded in plastic, the heat dissipation elements of each individual component become rendered ineffective.
FIG. 2A illustrates another design that utilizes surface mount components (mounted on copper) for a MOSFET device (high side 11 and low side 12) and a driver/controller 10 for a DC to DC converter system. However, this solution is not a complete power management system, as it does not include the passive components required in such a system.
FIG. 2B illustrates the packaged top side 20 of the design of FIG. 2A and an x-ray view 30 from the same perspective.
FIG. 2C illustrates a package mechanical drawing of the design of FIGS. 2A and 2B. Package bottom view 34 illustrates the metal bottom, or lead frame, used has a heat sink (31, 32 and 33). Unfortunately, this design does not provide a complete system solution because the passive components required for a complete design are not included.